2008 BMW 135i Speaker Sizes

The 2008 BMW 135i factory audio system contains specific speaker locations. The front door panel accommodates a 0.75 inch speaker size alongside a 4 inch unit, while the rear deck lid supports 4 inch speakers. Below seats locations accept 8 inch units. Compatible speaker types for replacement and upgrade include tweeter, midrange, and subwoofer components.

Specific details regarding locations, speaker sizes, and types are outlined in the compatibility chart.

Speaker Details by Location
Location Size Type Notes
Below Seats 8 Subwoofer
  • Very limited height clearance
  • Medium replacement priority
  • Replacement difficulty: medium
Front Door Panel 0.75 Tweeter
  • Standard installation
  • High replacement priority
  • Replacement difficulty: low
Front Door Panel 4 Midrange
  • Standard installation
  • High replacement priority
  • Replacement difficulty: low
Rear Deck Lid 4 Midrange
  • Access through trunk
  • Medium replacement priority
  • Replacement difficulty: low

2008 BMW 135i Speaker Replacement Summary

4 total positions
3 easy to replace
2 high priority
0 professional only

Replacement difficulty:

Low: 3 Medium: 1 High: 0

Replacement priority:

High: 2 Medium: 2 Low: 0

2008 BMW 135i Radio Slot Size (DIN)

DIN Type Size (inch) Size (mm) Notes
Single DIN or Double DIN 7"×2" or 7"×4" 180×50 or 180×100 Vehicle supports both radio sizes
  • Always measure the slot before purchasing a new radio
  • Check slot depth - it may vary

Additional Notes

  • The 2008 BMW 135i features a multi-component speaker arrangement with separate tweeters and midrange drivers in the front doors, suggesting a factory system designed for frequency-specific sound reproduction rather than full-range coaxial speakers.
  • Replacing the 0.75-inch tweeters in the front door panels may offer potential improvements in high-frequency clarity and detail, particularly when paired with upgraded 4-inch midrange drivers that handle mid-frequency content.
  • The factory 4-inch midrange speakers located in both the front door panels and rear deck lid indicate a consistent speaker size across multiple locations, which could simplify replacement planning when considering aftermarket options.
  • An 8-inch subwoofer positioned below the seats provides factory low-frequency reinforcement, though this location beneath the seating area might limit both access for replacement and available installation depth for aftermarket alternatives.
  • The rear deck lid placement of 4-inch midrange speakers typically provides ambient fill and soundstage width, though these locations often receive less priority than front speakers when considering staged upgrades.
  • The component-style configuration in the 2008 BMW 135i, with separated tweeters and midrange drivers, generally allows for more precise soundstaging and imaging compared to coaxial designs where all drivers share a common mounting point.
  • The radio supports both single DIN and double DIN head unit configurations, providing flexibility for aftermarket receiver upgrades that might include enhanced amplification or signal processing capabilities to drive replacement speakers.
  • The relatively small 4-inch size of the midrange drivers throughout the cabin suggests these speakers likely require crossover support or supplementation from the subwoofer to achieve fuller frequency response, particularly in the lower midrange.